Olefin Metathesis for Effective Polymer Healing via Dynamic Exchange of Strong Carbon–Carbon Double Bonds

In this article, we demonstrate transition-metal-catalyzed olefin metathesis as a simple, effective method for healing polymers via dynamic exchange of strong carbon–carbon double bonds. Upon introducing a very low level of the Grubbs’ second-generation Ru metathesis catalyst into cross-linked polybutadiene (PBD) network, the material self-heals effectively at various conditions under moderate pressures. In sharp contrast, catalyst-free control samples with identical network topology and cross-linking density show minimal healing. The healing efficiency of the materials was carefully investigated under different concentrations of the Ru catalyst, compression pressures, and temperatures. It is demonstrated for the first time that a bulk polymer could effectively heal via dynamic covalent bond formation at sub-ambient temperature. The Ru-loaded PBD samples not only heal well with themselves but also with control samples without any catalyst. Furthermore, a completely Ru-free PBD network can heal effectively upon simply applying a very small amount of Ru catalyst only at the fracture surface. The simplicity and effectiveness of this self-healing approach make it potentially applicable to a wide range of olefin-containing polymers.

Covalent Mechanochemistry: Theoretical Concepts and Computational Tools with Applications to Molecular Nanomechanics

Covalent Mechanochemistry: Theoretical Concepts and Computational Tools with Applications to Molecular Nanomechanics



Jordi Ribas-Arino *† and Dominik Marx *†

^† Lehrstuhl für Theoretische Chemie, Ruhr−Universität Bochum, 44780 Bochum, Germany

A Polymer Surfactant Corona Dynamically Replaces Water in Solvent-Free Protein Liquids and Ensures Macromolecular Flexibility and Activity

The observation of biological activity in solvent-free protein–polymer surfactant hybrids challenges the view of aqueous and nonaqueous solvents being unique promoters of protein dynamics linked to function. Here, we combine elastic incoherent neutron scattering and specific deuterium labeling to separately study protein and polymer motions in solvent-free hybrids. Myoglobin motions within the hybrid are found to closely resemble those of a hydrated protein, and motions of the polymer surfactant coating are similar to those of the hydration water, leading to the conclusion that the polymer surfactant coating plasticizes protein structures in a way similar to hydration water.

Structured spheres generated by an in-fibre fluid instability

From drug delivery1, 2 to chemical and biological catalysis3 and cosmetics4, the need for efficient fabrication pathways for particles over a wide range of sizes, from a variety of materials, and in many different structures has been well established5. Here we harness the inherent scalability of fibre production6 and an in-fibre Plateau–Rayleigh capillary instability7 for the fabrication of uniformly sized, structured spherical particles spanning an exceptionally wide range of sizes: from 2 mm down to 20 nm. Thermal processing of a multimaterial fibre8 controllably induces the instability9, resulting in a well-ordered, oriented emulsion10 in three dimensions. The fibre core and cladding correspond to the dispersed and continuous phases, respectively, and are both frozen in situ on cooling, after which the particles are released when needed. By arranging a variety of structures and materials in a macroscopic scaled-up model of the fibre, we produce composite, structured, spherical particles, such as core–shell particles, two-compartment ‘Janus’ particles11, and multi-sectioned ‘beach ball’ particles. Moreover, producing fibres with a high density of cores allows for an unprecedented level of parallelization. In principle, 108 50-nm cores may be embedded in metres-long, 1-mm-diameter fibre, which can be induced to break up simultaneously throughout its length, into uniformly sized, structured spheres.

Single siRNA Nanocapsules for Enhanced RNAi Delivery

Synthetic siRNA has been considered as a highly promising therapeutic agent for human diseases. However, clinical use of siRNA has been hampered by instability in the body and inability to deliver sufficient RNA interference compounds to the tissues or cells. To address this challenge, we present here a single siRNA nanocapsule delivery technology, which is achieved by encapsulating a single siRNA molecule within a degradable polymer nanocapsule with a diameter around 20 nm and positive surface charge. As proof-of-concept, since CCR5 is considered a major silencing target of HIV therapy, CCR5–siRNA nanocapsules were delivered into 293T cells and successfully downregulated the CCR5 RNA fused with mCherry reporter RNA. In the absence of human serum, nanocapsules and lipofectamine silenced expression of CCR5–mCherry expression to 8% and 15%, respectively. Such nanocapsules maintain the integrity of siRNA inside even after incubation with ribonuclease and serum for 1 h; under the same conditions, siRNA is degraded in the native form or when formulated with lipofectamine. In the presence of serum, CCR5–siRNA nanocapsules knocked down CCR5–mCherry expression to less than 15% while siRNAs delivered through lipofectamine slightly knocked down the expression to 55%. In summary, this work provides a novel platform for siRNA delivery that can be developed for therapeutic purposes.

Cable-Type Flexible Lithium Ion Battery Based on Hollow Multi-Helix Electrodes

The mechanical flexibility of a cable-type battery reaches levels far beyond what is possible with conventional designs. The hollow-spiral (helical) multi-helix anode architecture is critical to the robustness under mechanical stress and facilitates electrolyte wetting of the battery components. This design enables the battery to reliably power an LED screen or an MP3 player even under severe mechanical twisting and bending.

A Yolk–Shell Nanoreactor with a Basic Core and an Acidic Shell for Cascade Reactions

Hollow nanoparticles with movable core, which have an acidic and a basic shell core were, using a selective etching method supported organosilane prepared and used as efficient nanoreactors in catalysis of a Deacetalisierungs / Henry cascade reaction with high activity and selectivity. This strategy is promising for the design of multi-functional nanoreactors for cascade reactions.

Bioactive Polymeric Metallosomes Self-Assembled through Block Copolymer–Metal Complexation

Spontaneous formation of polymeric metallosomes with uniform size ( 100 nm) was found to occur in aqueous medium through the reaction of an anticancer agent, (1,2-diaminocyclohexane)platinum(II) (DACHPt), with a Y-shaped block copolymer of ω-cholesteroyl-poly(l-glutamic acid) and two-armed poly(ethylene glycol) (PEGasus-PLGA-Chole). Circular dichroism spectrum measurements revealed that the PLGA segment forms an α-helix structure within the metallosomes, suggesting that secondary-structure formation of metallocomplexed PLGA segment may drive the self-assembly of the system into vesicular structure. These metallosomes can encapsulate water-soluble fluorescent macromolecules into their inner aqueous phase and eventually deliver them selectively into tumor tissues in mice, owing to the prolonged blood circulation. Accordingly, fluorescent imaging of the tumor was successfully demonstrated along with an appreciable antitumor activity by DACHPt moieties retained in the vesicular wall of the metallosomes, indicating the potential of metallosomes as multifunctional drug carriers.

In Vivo Encapsulation of Nucleic Acids Using an Engineered Nonviral Protein Capsid

In Nature, protein capsids function as molecular containers for a wide variety of molecular cargoes. Such containers have great potential for applications in nanotechnology, which often require encapsulation of non-native guest molecules. Charge complementarity represents a potentially powerful strategy for engineering novel encapsulation systems. In an effort to explore the generality of this approach, we engineered a nonviral, 60-subunit capsid, lumazine synthase from Aquifex aeolicus (AaLS), to act as a container for nucleic acid. Four mutations were introduced per subunit to increase the positive charge at the inner surface of the capsid. Characterization of the mutant (AaLS-pos) revealed that the positive charges lead to the uptake of cellular RNA during production and assembly of the capsid in vivo. Surprisingly, AaLS-pos capsids were found to be enriched with RNA molecules approximately 200–350 bases in length, suggesting that this simple charge complementarity approach to RNA encapsulation leads to both high affinity and a degree of selectivity. The ability to control loading of RNA by tuning the charge at the inner surface of a protein capsid could illuminate aspects of genome recognition by viruses and pave the way for the development of improved RNA delivery systems.

A Novel Electromechanical Actuation Mechanism of a Carbon Nanotube Fiber

 

A spun carbon nanotube fiber functions as a torsional actuator in almost all available environmental media such as air, water, organic solvents, and electrolyte solutions. The Ampere's Law among helically aligned carbon nanotubes explains the simultaneous occurrence of lengthwise contraction and rotary torsion upon applying a low current. The produced stress is over 100 times that of the strongest natural skeletal muscle with high reversibility and good stability. The use of torsional fibers for electric motors is demonstrated.

Porphyrin Shell Microbubbles with Intrinsic Ultrasound and Photoacoustic Properties

 
Porphyrin–phospholipid conjugates were used to create photonic microbubbles (MBs) having a porphyrin shell (“porshe”), and their acoustic and photoacoustic properties were investigated. The inclusion of porphyrin–lipid in the MB shell increased the yield, improved the serum stability, and generated a narrow volumetric size distribution with a peak size of 2.7 ± 0.2 μm. Using an acoustic model, we calculated the porshe stiffness to be 3–5 times greater than that of commercial lipid MBs. Porshe MBs were found to be intrinsically suitable for both ultrasound and photoacoustic imaging with a resonance frequency of 9–10 MHz. The distinctive properties of porshe MBs make them potentially advantageous for a broad range of biomedical imaging and therapeutic applications.